Photochemical para Rearrangement of Phenyl Ethers

Kharasch, M. S.; Stampa, Guido; Nudenberg, W.

doi:10.1126/science.116.3012.309

“…47 O intermediário é instável, e o ceto-enol formado ocorre por tautomerização para gerar fenol orto-substituído. Por outro lado, Kharasch et al, 48 relataram em 1952 que fotoirradiação desencadeou os rearranjos de fenil alil e éteres benzil fenil nos estados excitados eletrônicos; esta reação foi assim chamada rearranjo de Claisen fotoquímico. O mecanismo proposto pelos autores é mostrado no esquema 15b.…”

Section: Rearranjo De Claisen (Oxa-cope)unclassified

The most Used Claisen Rearrangements in Organic Synthesis: A Review

Filho

¹

,

Fraitas

²

,

Freitas

³

et al. 2017

Rev. Virtual Quim.

0

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This manuscript is a literature review of major [3,3]-sigmatropics rearrangements, but specifically Claisen rearrangement, commonly used in organic synthesis over the past 16 years. Rearranged products result from a thermodynamic stability facet. In pericyclic reactions the term sigmatropic shift or sigmatropic rearrangement is better suited than rearrangement. Claisen s rearrangements are among the most well-known pericyclic reactions governed by the WoodwardHoffmann rules. The principles of Claisen rearrangements and their mechanisms are treated in the present study.Keywords: Organic synthesis; rearrangements; Claisen rearrangements. ResumoEste manuscrito trata-se de uma revisão bibliográfica sobre os principais rearranjos [3,3]-sigmatrópicos, mas especificamente rearranjos de Claisen, mais usados em síntese orgânica nos últimos 16 anos. Produtos rearranjados resultam em uma estabilidade termodinâmica. Em reação pericíclica o termo "deslocamento sigmatrópico" ou "rearranjo sigmatrópico" é mais adequado do que simplesmente rearranjo. Os rearranjos de Claisen são as reações pericíclicas mais conhecidas, dentre as quais obedecem à regra de Woodward-Hoffmann. Neste estudo foram examinadas além dos rearranjos os seus mecanismos.Palavras-chave: Síntese Orgânica; rearranjos; rearranjos de Claisen.

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“…3) Although this interpretation of the photo-Claisen rearrangement was highly attractive, the following facts seemed to us conflicting enough to warrant a thorough reinvestigation of the photo-rearrangement of allyl phenyl ethers:…”

mentioning

confidence: 99%

“…

Two years ago, Woodward and Hoffmann presented an ingenious theory in an attempt to interpret the stereochemical cours of the so-called "electrocyclic" and "sigmatropic" transformations.1) They suggested1b) that the photo-Claisen rearrangement reported to give a para-rearrangernent product2) would serve as an example of the [3,5] sigmatropic transformation.Another example of the photo-Claisen rearrangement had previously been reported to give only a pararearrangement product.3)Although this interpretation of the photo-Claisen rearrangement was highly attractive, the following facts seemed to us conflicting enough to warrant a thorough reinvestigation of the photo-rearrangement of allyl phenyl ethers:(1) An eight-membered cyclic transition state these systems seems sterically impossible.(3) Several related systems, phenyl esters,4) acyl anilides,5) phenoxyacetic acid,6) and ethyl phenyl carbonate,7) have been reported to rearrange photochemically to ortho-and para-rearrangement products.The recent publication of a communication8) dealing with an investigation closely related to ours prompts us to publish our own results.

ExperimentalMaterials. The allyl phenyl ethers for the photoreaction were purified by rectification until no appreciable impurity was observed by glc.

Reaction Procedure.

…”

mentioning

confidence: 99%

“…Two years ago, Woodward and Hoffmann presented an ingenious theory in an attempt to interpret the stereochemical cours of the so-called "electrocyclic" and "sigmatropic" transformations.1) They suggested1b) that the photo-Claisen rearrangement reported to give a para-rearrangernent product2) would serve as an example of the [3,5] sigmatropic transformation.…”

mentioning

confidence: 99%

“…tions.1) They suggested1b) that the photo-Claisen rearrangement reported to give a para-rearrangernent product2) would serve as an example of the [3,5] sigmatropic transformation.…”

mentioning

confidence: 99%

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Photo-Claisen Rearrangement. The Photochemical Rearrangement of Allyl Phenyl Ethers

Koga¹,

Kikuchi²,

Koga³

1968

Bulletin of the Chemical Society of Japan

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Two years ago, Woodward and Hoffmann presented an ingenious theory in an attempt to interpret the stereochemical cours of the so-called "electrocyclic" and "sigmatropic" transformations.1) They suggested1b) that the photo-Claisen rearrangement reported to give a para-rearrangernent product2) would serve as an example of the [3,5] sigmatropic transformation.Another example of the photo-Claisen rearrangement had previously been reported to give only a pararearrangement product.3)Although this interpretation of the photo-Claisen rearrangement was highly attractive, the following facts seemed to us conflicting enough to warrant a thorough reinvestigation of the photo-rearrangement of allyl phenyl ethers:(1) An eight-membered cyclic transition state these systems seems sterically impossible.(3) Several related systems, phenyl esters,4) acyl anilides,5) phenoxyacetic acid,6) and ethyl phenyl carbonate,7) have been reported to rearrange photochemically to ortho-and para-rearrangement products.The recent publication of a communication8) dealing with an investigation closely related to ours prompts us to publish our own results. ExperimentalMaterials. The allyl phenyl ethers for the photoreaction were purified by rectification until no appreciable impurity was observed by glc.Reaction Procedure. A 5% solution of a sample in isopropyl alcohol was irradiated with an immersiontype 10W low-pressure mercury lamp (Ricoh Kagaku Sangyo Co., UVL300Q) under a nitrogen atmosphere. After irradiation, most of the solvent was removed under reduced pressure, and the residual mixture was analyzed by glc.Identification of Products. o-and p-Allylphenols, 2-allyl-3,5-dimethylphenol, trans-o-and -p-but-2-enylphenols, and o-and p-(1-methyl-prop-2-enyl)phenols were identified by a comparison of their retention times with those of authentic sample. 4-Allyl-3,5-dimethylphenol was isolated from the reaction mixture by means of preparative glc and was identified spectrometrically. Two unknown peaks in the gas chromatogram of the reaction mixture from traps-but-2-cnyl phenyl ether were tentatively assigned to cis-o-and -p-but-2-enylphenols on the basis of their having been formed by the irradiation of their trans-isomers.Analyses. The samples were analyzed by the use of a Hitachi K-23 gas chromatograph. A 1-meter Celite-545 (60-80mesh) column with 33% Silicon KF-54 was used. The results in the table are given as the percentage ratio of the peak area. Results and DiscussionAs shown in the table, all the compounds rearranged to give ortho-and para-rearrangement products in addition to the parent phenols of the starting ethers. Some unidentified products were also present. trans-But-2-enyl phenyl ether was shown to give o-and p-but-2-enyl and o-and p-(1-methylprop-2-enyl)phenols.The results are consistent with those of Schmid2) and clearly indicate that the rearrangement does not proceed *1 A preliminary account of this investigation has been presented at

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